Flip chips are microelectronic devices in which a silicon chip, or die, is attached facedown to a substrate via a plurality of small solder bumps. In general, a die attach system “picks and places” the die directly from a silicon wafer and places the die on the substrate using a plurality of solder bumps to form an electrical connection between the two. Once the solder has been reflowed and solidified, a non-conductive underfill material is typically inserted into the gap between the die and substrate to strengthen the connection between the two and to provide a barrier to moisture or other contaminants.
As chip sizes have decreased over time, flip chip assemblies have also decreased in size. These smaller chip sizes require narrower bump pitches and, therefore, smaller bump sizes. This typically results in the flip chip having a decreased stand-off height between the die and the substrate, which may increase the level of stress at the connection between the solder bumps and the die due to the differences in the coefficients of thermal expansion (CTE) of the die and the substrate. Additionally, the decreased stand-off height may make inserting an underfill material between the die and substrate more challenging as many underfill materials resist flowing between a die and substrate with a small stand-off height.